After effectively testing the tag issue due to level differences between my Lv. 50, and moving down to a Lv. 42, I can in fact say that I have noticed a difference in the drops, not by much, but enough to tell. I will have to agree with the OP.
Firstly, I feel that since General Hex is considered the second toughest of Jolly's generals, and now has an Exclusive Legendary doll, it would at least warrant bumping him into the level range of his big brother, General Darkhart. A simple tweak (from a choice standpoint), changing his meager 23-30 level range up to something more threatening, let's say 26-33, or even up to Darkhart's 28-35 would be that General Hex would no longer appear Green to higher leveled players, and instead have a basic minimum of appearing with a Yellow nametag, which definitely drives up loot chances by a little bit.
Secondarily, I feel as if the argument in which bumping Hex's level is a bad choice due to the fact that there is an active quest linked with the boss,is currently bloated far more than it needs to be. Seeing as General Hex is not only easy to locate and travel to, and is also now linked with a Legendary drop (obviously), the method of completing the quest would be just the same as a player of average level looking to defeat Darkhart in the easiest manner possible. If you're level 25 and you're looking to beat the snot out of a boss without being forced to do it solo, what do you do? You go to
Abassa and you walk to the large group of players crowding and blowing the boss to bits.
Hex also has a huge Achilles Heel in which he is a Voodoo Doll user himself, meaning, take a player with any sort of weapon that can drain voodoo from the boss, and in no time at all the boss is stuck using the lower voodoo casts due to a constant lack of sufficient voodoo.
Counter Claim/s
A more personal gripe over anything, I feel like the methodology behind obtaining the Doll is flawed either way you dice it. Higher level players can't obtain it on a regular basis (by legendary standards) due to a level fluctuation, and lower level players (in which the surrounding area caters to) have an
Absolute 0% chance in obtaining the Doll up until a minimum of Level 25 in both Doll
AND Notoriety, far past the point in which Misty Mire is actively viable.